Method for the testing of detonating fuse



July 16,1935, w. o. SNELLING 2,008,045

METHODLFOR THE'IESTING 0F DETONM'ING FUSE Filed Nov. 18, 1931 INVVENTOR I Patented July 16,1935

UNITED sr T-Es PATENT OFFICE METHOD FOR THE TESTING OF DETONATING FUSE Walter 0. Snelling, Allentown, Pa., 'asslgnor to 1 grojan Powder Company, a corporation of New ork Application November 18, 1931, Serial No. 575,711

t Claims. .40]. 175-183) pal object of my invention is tov provide non-de-' structive means for determining the detonable continuity of the explosive or detonable core of detonating fuse, in connection with the manufacture of such fuse'and as a means of testing and checking the functionability of cordeau prior,

to its actual use. I

Cordeau or detonating fuse consists essentially of a core or ti-sin" of a'detonable explosive material such as trinitrotoluene, picric acid, nitropentaerythrite, trinitrophenyl-methyl-nitramin, or like substance or mixture of substances capable of transmitting adetonating wave at a very so high velocity,-this train of detonable material being encased in atube of lead, tin, or other suitable protective metal or alloy. It is widely used. in the explosives art as a means of transmitting detonation from one point to another, and particularly as a means for bringing about the practically simultaneous detonation of a large numbeioi separatedcharges of explosive. The type of cordeau in mostoommon use at the present time contains a core of trlnitrotoluene in a casing of lead, and this type of cordeau transmits a detonating wave at a rate of approximately 5300 meters per second, or roughly three miles per sec-' and.

For the purpose for which cordeau is technically used, it is highly important that it should function with absolute reliability. The failure of any portion oi. a length of cordeauto transmit a detonating wave to other portions of the blast in which it is used as a connecting means is usually followed lay serious consequences, and in addi tion to the expense which is involved insuch a failure to properly function, there is, also an element of hazard in the subsequent handling of the missed holes which it is very desirable to avoid.

' In the manufacture of cordeau a tube of malleable metal is first filled with the detonable agent in molten or semi-moltencondition, and after the detonable agent has cooled and wholly or partly solidified the metal tube with the contained core w r detonable agent is subjectedto a drawing, rolling or swaging operation, to' increase its length and decrease its diameter to form cordeau of the. desired final size. It has long been known that, any cavitation caused by the presence of air bubbles in the fluid or semi-fiuidtrinitrotoluene or 5 other detonable material used to fill the initial tube is very likely to result in the final cordeau being defective, this being due to the fact that although such a detonable agent as trinitrotolucue, for example, possesses very great explosive strength, it is quite incapable 'of jumping any considerable air gap or of detonating through a column of very small diameter. The'outside diameter ofcommercial cordeau is usually 6 mm.,

and the wall thickness of the lead tube is 0.8 mm.,

so that accordingly the actual diameter of the cylindrical detonable core of trinitrotoluene is normally but 4.4 mm. Although a continuous core or train of trinitrotoluene 4.4 mm. in diameter will transmit a wave of detonation for indefinlte'distances, careful tests have shown that an airgap of but eight millimeters in such a column oftrinitrotoluene makes the functioning of thevcordeau very doubtful, while an air gap of ten millimeters or more inevitably results in the failure of the detonating wave to pass such space or gap. Similarly, any marked (and particularly any irregular) reduction in diameter of the core of trinitrotoluene is likely to result in failure of detonation to continue through the entire column of detonable material.

Manufacturers of cordeau have recognized the extremely serious consequences of any cavitation in cordeau, and it has long been known that the presence of air bubbles, open spaces or reduction in diameter of the core in a line of cordeau would entirely prevent the proper functioning of such material. Due to the fact that trinitrotoluene shrinks very greatly on solidifying; the possibility of shrinkage openings or cavities is a se- 40 rious one, and many ingenious methods have been suggested and used for the purpose of insuring the complete filling of the lead tube with explosive, and for the purpose of avoiding the presence of any air bubbles, open spaces orlengths of explosive'core of constricted diameter within the finished cordeau. ll'otwithstanding the great care which has been taken by manufacturers of cordeau to insure the absence of any open spaces or air bubbles the column of i and cannot prove the detonable continuity of the.

trinitrotoluene incordeau it has been found difficult, to prevent the occasional presence of lengths of core of constricted diameter in the flnished product.

Up to the time of my present invention no method had been found for the commercial testing of the detonable continuity of the normally hidden or invisible inner core'of explosive material,present in cordeau, turers of cordeau have developed a number of excellent tests for the purpose of showing the proper functioning of cordeau, all of these tests depend upon the detonation of the cordeau and thus destroyjthe material in the course ofmaking' the test. The most common test for cordeau is known as the zigzag test, and consists in fastening together a number of short lengths of cordeau at right angles to each other by approved splices or connections, and then initiating a detonating wave at one end of the "zigzag" thus formed. Cordeau of satisfactory sensitive ness detonatessatisfactorily through the successives splices or connections represented by the zigzag and cordeau represented by samples which passes this test is assumed to be of satisfactory grade for use, although'careful consideration of this test will of course show that it does not core of any portion of the cordeau except the portion actually used in the test, and which isdestroyed inthe course of making the test.

My invention provides means for the accurate determination of the cross-sectional area of the detonable core of trinitrotoluene or other agent in cordeau by an entirely non-destructive method of testing, and enables the manufacturer of cordeau to detect the presence of lengths of materialof constricted core diameter within a column of cordeau without actually idetonating the cordeau or opening the lead tube or otherwise injuring or destroying the material.

When a metal tube containing a uniform filling charge of a detonable agent is rolled, drawn or swaged to form cordeau, there is a'definite relationship between the lengthening of the metal tube, the wall thickness of the resultant point any resisting means to prevent the thick- -ening of the wall of the metal tube, and at such point the wallthickness of the metal tube will greatly exceedthe normal wall thickness present at other portions along the length of the tube. My invention relates primarily to meansfor determining the cross-sectional area of the contained core of detonable material through nondestructive methods of measuring the wall thickness of the outer casing orsheath of cordeau by means of electrical effects produced within such metal tube.

In the drawing forming part of this application Figure l isa plan view of a section through a piece of cordeau of normal structure. Figure 2 is-a corresponding section through alen'gth of cordeau in which an air bubble originally existed Figure 3' is a diagrammatic'representation. of one form of apparatus suitable for the prac- I Although manufactice of my present invention. Figure 4 is 9. diagrammatic representation of another form of apparatus suitable for the practice of my present invention.

In Figure 1, I is the detonable column of trinitrotoluene or other detonation-transmitting explosive material in a normal piece of cordeau and 2 is the tube or sheath of lead or other casing material. In Figure 2, I is the detonable col-v umn of explosive material as it normally exists throughout the length of the cordeau when no openings or cavities are present in theinitial filling material, while Ia shows a constriction such as occurs afterthe cordeau has been subjected to a rolling, drawing or swaging operation, from the presence of a small bubble'of air in the initial filling charge. 2 is the lead tube showing the normal wall thickness, while 2a shows the greatly thickened ,wall at a point where theinner detonable core is constricted because of the original presence of an open space or an air bubble in the initial tube before being reduced to its final diameter.

In Figure 3,3 is a length of cordeau undergoing test in accordance with one form of my present invention. 4 is an electrode. consisting of a number of tufts of wire or other electrically-conducting material suitably encased in an electrode going test, 9 is a solenoid energized by alternating current of high frequency applied at the terminals 9a and 9b from any suitable source, I 0 is a thermo-- battery or plurality of thermo-couples, each thermo-couple having one junction adjacent to the line of cordeau 3 and 8 is an ammeter or other instrument for measuring theelectric' current or electrical potential produced in thermo-battery III, the thermo-battery IIi being connected to the in Figure 3. the cordeau is continuously passed between the two electrodes 5 and 51:, contact being effected withthe brushesl and la. A difference of electrical potential created by battery 1 causes an electric current to flow in the closed circuit existing within the system, the cordeau forming the return portion of the circuit. As long as the wall thickness of the lead tube remains eonstantthe conductivity of the system when considered as a whole'will similarly remain constant, and ammeter 8. will indicate a. definite amount of current passing through the system, the exact quantity of current depending of course upon the electrical resistance of the various elements of the circuit and the electrical diflference of potential created by battery I. When a portion of cordeau having a constricted core of deton- I able material passes through the testing apparatus, however, ammeter 8 will momentarily show a greatly increased current within the circuitat the time that the portion of the cordeau having marily for the purpose of illustrating the. prim,

ciple of the present invention of employing the electrical characteristics of the thickened lead.

walls of cordeau at a point in which a constriction plosive core.

of the detonable core exists as an indirect means of detecting or of indicating the existence-oi such ing of a sole oid and measuring apparatus of known type. 11 one convenient formjof appa ratus the line of cordeau is progressively passed through two closely adjacent solenoids through which alternating currents of high frequency are passing in balanced circuits, such as two coupled oscillating dynatron circuits for example- Any inequality in the thickness of the explosive core will be indicated by a lack of balance in the oscillating circuits when the portion of the metallic sheath having walls of excess thickness passes between the two solenoids and this lack of balance of the oscillating circuits can be indicated by beats and squeals. in an inductively .con-

- nected loud speaker or in any other of the well known methods of indicating variations in current flow in high frequency oscillating circuits. In still another form of apparatus the line of cordeau, may be passed progressively through two closely adjacent solenoids through only one of which an oscillating current is passing. This oscillating current will produce eddy currents within the metal of the sheath, and themagnitude of these eddy currents will be materially modified when portions of the cordeau having a constricted diameter 'of'explosive core, and a correspondingly thickened portion of metallic sheath, passes through the solenoid energized by'the oscillating current. The adjacent but electrically disconnectedsolenoid will be influenced by the magni-' tude of the eddy'currents within the metallic sheath, and will pick up an oscillating electric current the magnitude of which will be proportional tothe eddy currents themselves, and this secondary current can be utilized in any of the known forms of electrical'devices as a means of indirectly determining the uniformity of .the ex- Instead oflammeteror voltmeter 8 as shownin Figures 3 and 4 a wide variety of current actuated devices may be used,-such for example as a relay which will remain in one position when such minimum of current is passing as corresponds to the passage of tubing of normal wall thickness, but which will be actuated or moved to a second position by the increased current which passes when cordeau having a constricted column of a detonable material and consequently thickened metal walls passes through the apparatus.

The apparatus shown in Figure 4 represents an embodiment of my present invention in which metal sheath of the length of cordeau 3, and in the absence of any means for removing or utilizingthese eddy currents within the metal, they I, are transformed into heat, slightly increasing the temperature. of the 'metallic sheath... The

thermo-battery HI' creates a constant difference of potential which is proportional to the temperature of the cordeau, and this diil'erenceof potential is measured by voltmeter 8. If the line of cordeau is passed through the apparatus from .left to rightat a constant rate, measuring instru ment 8 will remain constant, but upon any portion of cordeau having a restricted diameter of explosive core passing through the apparatus it will show a fluctuation, due to the diiference in temperature created by the modified eddy currents resulting from the thickening of the metal walls of the cordeau at the portion where the explosive core is constricted in diameter.

As means for creating acoustical, actinic, electrical and mechanical effects from any given change of electric flow are well known in the art I will not attempt to enumerate the many em bodiments of my invention whichare possible by ,the use, of well known equivalents for the forms herein described, but it will be evident to those familiar with the art that instead of the use of a. galvanometer, ammeter, or voltmeter as a means of measuring or indicating the secondary electrical effects produced in accordance with my invention, lights may be flashed, bells maybe sounded, horns may be operated, or control apparatus for the purpose of marking the portion of cordeau which is defective, or of stopping the further motion of the testing apparatus, may be actuated, or any other suitable visible, audible or operative device may be set in motion oroperation, in accordance with well known inspection methods.

I As it will be evident that many modifications may be made without departing from the principles of the disclosure as herein made, no limitations are to beplaced upon my invention except such as are indicated in the appended claims.

, I claim:

1. The process'of testing the continuity of the core of detonable material in cordeau which comprises establishing electricalforces within a metallic sheath surrounding such core and measuring the intensity of such electrical forces.

2. The process of testing the continuity-of the core of detonable material in cordeau which comprises establishing a flow of electricity within a metallic sheath surrounding such core andmeasuring the rent;

3. The process of testing the continuity of a core of a detonable material compressed within an associated metallic sheath of a malleable metal which comprises establishing an electro-magnetic field adjacent to the metallic sheath and measurintensity of the resulting electric cur- ,ing the electrical efiect produced by the action of suchaalectro-magnetic field upon the metallic sheath.

4. The process of testing the uniformity of cross-sectional area of a core of a detonable material encased in an associated metallic sheath which comprises creating a difference of electrical potential at two points along the length of the metallic sheath and measuring the intensity of the electrical flow thereby created.

5. The process of testing the uniformity of cross-sectional area of a core of a detonable material encased in an associated metallic sheath which comprises establishing a flow of electric current within the metallic sheath and measuring the intensity of such electric flow as a-meas- 'ure of the cross-sectional area of the explosive material.

6. The process of testing the uniformity of cross-sectional area of a core of a detonablemacross-sectional area of a core of a detonable material encased in a; metallic sheath whichcome prises creating eddy currents within the metallic sheath by the action of an oscillating electric current exterior to the metallic-sheath and electrically insulated irom same and employing the intensity of such eddy currents as a measure'of the cross-sectional area of the explosive material within the metallic sheath.

' ,WALTER O. SNELLING. 

